1. Field of the Invention
The present invention relates to a frequency multiplexer employing a blazed diffraction grating and, more particularly, to a frequency multiplexer which permits the bidirectional conversion of at least two intermediate angularly distinct planar wavefronts into a single directional wavefront by the use of a blazed diffraction grating mounted at the aperture of an antenna, where each distinct planar wavefront can correspond, for example, to the wavelength of a separate radio channel.
2. Description of the Prior Art
Various arrangements are known using stripline or waveguide elements such as, for example, branching filters for separating or multiplexing a plurality of radio channels comprising separate frequency bands. In this regard, see for instance, U.S. Pat. Nos. 3,428,918 issued to G. L. Matthaei on Feb. 18, 1969, and 3,698,001 issued to M. Koyama et al on Oct. 10, 1972.
U.S. Pat. No. 2,702,859 issued to C. V. Robinson on Feb. 22, 1955 discloses a directional microwave reflector type antenna comprising a reflector having small plates or zones to produce a scanning radiation beam having a planar wavefront when illuminated by a line source reciprocating normal to itself across the aperture of the reflector.
U.S. Pat. No. 3,108,279 issued to R. A. Eisentraut on Oct. 22, 1963, relates to a antenna reflector having different reflecting properties for incident electromagnetic radiation of different wavelengths. More particularly, the surface of the reflector is provided with small steps or grooves across the width thereof which focus incident waves within a desired wavelength range at the focal area of the reflector while reflecting incident waves of much shorter wavelength in a direction to avoid the focal area.
An article by K. B. Mallory et al entitled "A Simple Grating System for Millimeter and Submillimeter Wavelength Separation", IEEE Transactions on Microwave Theory and Techniques, Vol, 11, No. 5, September 1963, pages 433-434, describes an echelette grating spectrometer having rectangular facets set at a constant angle to the surface of the grating. There, two horn-fed parabolic reflectors are mounted with their axes intersecting at a predetermined angle. The axis of rotation of the grating is parallel to the long edges of the rectangular facets of the grating and by tilting the grating it is possible to reflect the desired wavelength to the receiving feedhorn while diverting the unwanted wavelengths out of the principal plane of the spectrometer.
An article entitled "A Grating Spectrometer for Millimeter Waves" by R. J. Coates in Review of Scientific Instruments, Vol. 19, No. 9, September 1948, pages 586-590, discloses an echelette grating spectrometer wherein the grating is formed to rotate about its axis in a manner whereby the normal distance between adjacent parallel flat reflectors changes as a result of this rotation. With this grating arrangement, energy, having a plane phase front, incident upon the grating is reflected back to the same position regardless of the grating angle. The signals associated with a sending and a receiving feedhorn are directed by a single curved reflector at the grating, and the angle corresponding to a peak received signal is read from the records and the wavelength calculated using a particular formula.